[TowerTalk] hose clamps and end caps

[donovanf at starpower.net]

I'm sorry my previous comment about stainless steel screws was
unclear.  I'll try again.

Yagi builders commonly use rivets, self-tapping stainless steel
screws, or hose clamps to join and secure telescoped aluminum tubing.  In each case, the fasteners draw the tubes together and increase the pressure between the tubes in the vicinity of the fastener.

Increased pressure reduces the RF resistance of the joint, especially
when NoAlox or other similar materials are used to control oxidation.

There's a common misconception that RF current flows through the
rivet or stainless steel screw; however, skin effect prevents the flow
of RF current through any fastener that penetrates the tubing. 

In a well constructed joint, skin effect confines RF current flow to
the location where the tip of the larger tube tightly contacts the
smaller diameter tube.  The RF resistance of the joint will increase
if the joint becomes loose or significantly oxidized, despite the
presence of a fastener that penetrates the tubing.

73
Frank
W3LPL








---- Original message ----
>Date: Mon,  3 Mar 2008 13:18:28 -0500 (EST)
>From: <donovanf at starpower.net>  
>Subject: Re: [TowerTalk] hose clamps and end caps  
>To: TOWERTALK at contesting.com
>
>Oops...
>
>While stainless steel screws may perform useful mechanical functions
>if applied correctly, they can NOT perform electrical functions at RF
>because of skin effect.
>
>73
>Frank
>W3LPL
>
>---- Original message ----
>>Date: Sun, 3 Feb 2008 09:52:39 -0600
>>From: "Bill Parry" <bparry at rgv.rr.com>  
>>Subject: Re: [TowerTalk] hose clamps and end caps  
>>To: <Cqtestk4xs at aol.com>, <TOWERTALK at contesting.com>
>>
>>Bill
>>
>>Did you still use the hose clamps too? I considered the SS screw idea but
>>decided that I would use the rivets instead. One hole in the element not
>>two. Years ago I used to use aluminum self tapping screws but I quit that
>>because I sheared a couple of those off.
>>
>>Bill
>>
>>-----Original Message-----
>>From: towertalk-bounces at contesting.com
>>[mailto:towertalk-bounces at contesting.com] On Behalf Of Cqtestk4xs at aol.com
>>Sent: Monday, March 03, 2008 9:41 AM
>>To: TOWERTALK at contesting.com
>>Subject: Re: [TowerTalk] hose clamps and end caps
>>
>>In a message dated 3/3/2008 2:41:31 P.M. Greenwich Standard Time,  
>>bparry at rgv.rr.com writes:
>>
>>had two  experiences that made me reconsider what I was doing. The first
>>was putting  up a KLM 15 6 element yagi.  It had been up for a few weeks
>>when
>>two  of the hose clamps popped and broke.  I have always thought that I  had
>>tightened them too tight and the extremes of the temperature here in  South
>>Texas had done the rest. The elements slowly slid out and fell to  the
>>ground. I began to worry about how tight I should be tightening  those
>>clamps. With a ratchet, it is easy to break or over-tighten hose  clamps.
>>(Incidentally, I would replace those hose clamps while the antenna  is
>>down.)
>>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 
>>My old KLM antennas used the hose clamp method.  I simply drilled a  small 
>>hole at each joint and inserted a small stainless screw covered with
>>NoAlOx.  
>>It helped to secure the joint as well as making a good electrical
>>connection.
>> 
>>Bill KH7XS/K4XS
>>
>>
>>
>>
>>
>>
>>
>>
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